1. Field
The present embodiments relate to a keyless entry system.
2. Related Art
Keyless entry systems can perform wireless communication between an on-vehicle device, which is installed in a vehicle, and a portable device, which is carried by users, so as to lock/unlock doors of the vehicle. Recently, passive keyless entry systems have been developed. In the passive keyless entry systems, upon detecting approach of a portable device to a vehicle, communication is automatically performed between an on-vehicle device and the portable device. The passive keyless entry systems lock/unlock doors of the vehicle after authenticating an ID uniquely set for each portable device. Unexamined Japanese Patent Application Publication No. 2002-77972 (US Patent Application Publication No. 2002/0025823) describes one such keyless entry systems.
It is important for passive keyless entry systems to be able to determine whether a portable device resides outside or inside of a vehicle. Thus, an on-vehicle device includes a plurality of transmitting antennas attached at various places of the vehicle. The on-vehicle device determines that the portable device resides inside the vehicle if the portable device receives a radio wave from the transmitting antennas attached inside the vehicle. Alternatively, the on-vehicle device determines that the portable device resides outside the vehicle if the portable device receives a radio wave from the transmitting antennas attached outside the vehicle.
However, in known keyless entry systems, accuracy of determination of positions of portable devices is not sufficient. For example, when a radio wave transmitted from a transmitting antenna attached inside a vehicle leaks outside the vehicle, the portable device may be mistakenly determined to reside inside the vehicle even if the portable device actually resides outside the vehicle. Conversely, when a radio wave transmitted from a transmitting antenna attached outside the vehicle leaks inside the vehicle, the portable device may be mistakenly determined to reside outside the vehicle even if the portable device actually resides inside the vehicle. If the radio wave transmission power is lowered in order to prevent the leakage of the radio wave, the portable device may not receive the radio wave even if the portable device is inside the vehicle. This may also cause the false determination.
A solution to this problem was described in Japanese Patent Application No. 2005-173219, which was filed by the assignee of the present patent document. An inside data group and an outside data group are obtained beforehand. The inside data group has intensity information of a plurality of signals transmitted from a plurality of transmitting antennas of the vehicle when a portable device is placed along an inner surface of the vehicle. The outside data group has intensity information of a plurality of signals transmitted from the plurality of transmitting antennas of the vehicle when a portable device is placed along an outer surface of the vehicle. Whether the portable device resides inside or outside the vehicle is determined by determining which of the inside data group and the outside data group the intensity data of the signal transmitted from each of the transmitting antennas and detected by the portable device closely resembles.
The transmitting antennas are attached to closable side mirrors of the vehicle. The inside data group and the outside data group are obtained with the side mirrors being opened. Thus, one embodiment of the above-cited application permits the determination of whether the portable device resides inside or outside the vehicle to be performed accurately if the side mirrors are opened.
However, if the side mirrors are closed, the strength of the signal detected by the portable device changes due to the change in the position of the transmitting antennas attached to the vehicle, which undesirably decreases the accuracy of the determination. This problem is not specific to a case where the transmitting antennas are attached to the side mirrors, and occurs when the transmitting antennas are attached to movable objects of the vehicle.
Even if the transmitting antennas are not attached to movable objects, movement of the movable objects may affect the radio wave transmitted from the transmitting antennas. In such a case, the strength of the signal detected by the portable device changes before and after the movement of the movable objects, which decreases the accuracy of the determination.
The determination of the position of the portable device is not limited to the determination of whether the portable device resides inside or outside the vehicle, and whether the portable device resides inside or outside of a boundary apart from the door by predetermined distance can also be determined. In such a case, a light may be turned on upon determining that the portable device is within a radius of a predetermined distance from, for example, the door.
Accordingly, a keyless entry system that can determine the position inside or outside a predetermined boundary, which is not limited to a boundary defining inside and outside of a vehicle, is desired.